In surface cutting of a workpiece using a rotating cutting tool such as a milling cutter and an end mill, a knife mark is left on a cut surface of the workpiece due to a height difference at a boundary between cutting edges or the like, and impairs quality of the cut surface. Therefore, conventionally measures to reduce harmful knife marks have been exclusively taken in surface cutting of a workpiece. In contrast, as shown in Patent Document 1, a method for decorating a surface of a workpiece by making good use of such a knife mark has been proposed. This decoration method aims to decorate a surface of a workpiece by rotationally cutting the surface of the workpiece by using a rotating cutting tool having cutting edges on an outer circumference and leaving a knife mark having a width of 5 mm or more and 150 mm or less.
In Example 1 of the abovementioned patent document, as shown in FIGS. 31A, 31B, and 32, by using a cutter block having a cutting diameter D of 125 mm and the number of cutting edges of 2, cutting was performed at the number of revolutions N of 2,000 rpm and a feed rate F of 40 m/min. As a result, a knife mark was left in a shape of rectangular embossments successively extending in a rotation axis direction. This knife mark had a width Wa of 10 mm, a depth d of 0.200 mm, and a ratio of depth d to width Wa (d/Wa) of 0.020. Moreover, in Example 3, by using a rotating cutting tool having a cutting diameter D of 150 mm and the number of cutting edges of 2, cutting was performed at the number of revolutions N of 1,000 rpm and a feed rate F of 30 m/min. A knife mark had a width Wb of 9.5 mm, a depth d of 0.150 mm and a ratio (d/Wb) of 0.016. According to the abovementioned decoration method, the rotating cutting tool has a very large cutting diameter as exemplified by 125 mm and 150 mm, and the knife mark has a small ratio of depth d (mm) to width W (mm) (d/W) as exemplified by 0.016 to 0.020. Since the ratio (d/W) is as small as mentioned above, a height different in embossments on a surface produced by the knife mark is not sufficiently large and the knife mark cannot give sufficiently aesthetic appearance as a decorative pattern.